Mozilla has released Thunderbird 3. You can read the release notes, or download the darn thing. "If you like Firefox's tabbed browsing, you're going to love tabbed email. Thunderbird 3's tabbed email lets you load emails in separate tabs so you can quickly jump between them. Search results open in a new tab too. New tools like our timeline and filtering tools will help you pinpoint the email you're looking for, whether it’s the one from yesterday, last month, or several years ago."

I would expect a friendly "Are you sure?" dialog if I exceed the reasonableness threshhold.

"You seem to be doing something crazy, like opening 100 messages at once. We think this is nuts and are giving you a chance to cancel this action. If you choose to continue we really will try and open 100 windows, but we have no idea if your computer can take that.